The fungi in this, the only order in the class, produce zoospores that swim by means of a single anteriorly directed flagellum with mastigonemes that are hollow. The group is a small one (about 25 species) that occurs in soil, fresh water and marine habitats as do the Chytridiales and Spizellomycetales. Some members of the group occur as hyperparasites on the oospores of Oomycetes and the zygospores of endomycorrhizal fungi. In the Hyphochytriales, there is a range of developmental types from holocarpic (Anisolpidium) to eucarpic (Rhizidiomcyes) to polycentric (see Hyphochytrium). Isolation of these organisms is accomplished using the same methods as for the Chytridiomycetes. Sexual reproduction is poorly known in the group.
The cell wall of Rhizidiomyces apoplysatus and Hyphochytrium catenoides are known to contain both chitin and cellulose; it would be interesting to know if this is true of all members of the group. The zoospores have a kinetosome and a non flagellum-bearing centriole, both being closely associated with the nucleus. Three groups of microtubules (see Cooney, Barr and Barstow, 1985) originate in the kinetosomal area and traverse the cell. Zoospores of the Hyphochytriales lack a microbody-lipid complex but have ribosomes that are aggregated around the nucleus and partially separated from the rest of the cytoplasm by endoplasmic reticulum.
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